Do google rankings get affected when you switch server?

Do google rankings get affected when you switch server?

I recently moved from shared hosting to VPS, and I think traffic has reduced little bit since then.
Is this normal, when you switch server, google will reduce your ranking?
If yes, how long does it take to retain original rankings?

Also, what is the basic road map of good SEO these days? Back links needed, on-page SEO, etc.
Thanks

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